Technical Field
The present invention relates to an iron-base sintered alloy material suitable for a valve seat insert of an internal combustion engine, and particularly to further improving wear-resistance, reducing aggressiveness to mated material, and improving radial crushing strength, of the iron-base sintered alloy material.
Related Art
A valve seat insert of an internal combustion engine is press-fitted into a cylinder head to secure air-tightness in a combustion chamber and cool a valve. The valve seat insert seats a valve for opening and closing an intake hole and an exhaust hole. Therefore, for example, the valve seat insert is beaten by the valve, worn away by sliding, heated by combustion gas, and corroded by combustion products.
Recently, an internal combustion engine for an automobile has been strongly requested to have a higher output power and a higher fuel efficiency. To satisfy the request, the valve seat insert to be used is under a severer environment. The valve seat insert is also strongly requested to have further improved wear-resistance.
With respect to such a request, for example, JP 2005-248234 A describes the following iron-base sintered alloy material for a valve seat insert. The material includes a Co-base inter-metallic compound having a particle diameter of 10 to 150 μm and hardness of 500 HP 0.1 or more and less than 800 HP 0.1 at an area ratio of 10 to 20%, and a Co-base inter-metallic compound having a particle diameter of 10 to 150 μm and hardness of 800 HP 0.1 or more and less than 1100 HP 0.1 at an area ratio of 15 to 35%. In the material, the Co-base inter-metallic compounds are dispersed at an area ratio of 25 to 55% in total. According to the technique described in JP 2005-248234 A, a valve seat insert having excellent wear-resistance and low aggressiveness to mated material is obtained.
WO 2009/122985A1 describes an iron-base sintered alloy material for a valve seat insert. The technique described in WO 2009/122985A1 is directed to an iron-base sintered alloy material having two kinds of hard-particles dispersed and contained therein. According to the technique described in WO 2009/122985A1, the iron-base sintered alloy material contains first hard-particles having an average primary particle diameter of 5 to 20 μm and second hard-particles having an average primary particle diameter of 20 to 150 μm. The first and second hard-particles are selectively used such that a difference in particle diameter between adjacent peak tops is from 15 to 100 μm among diameters corresponding to peak tops of mixed hard-particles obtained by mixing the first and second hard-particles. The first and second hard-particles are blended so as to occupy 10 to 60% by area in total. WO 2009/122985A1 describes that, as a result, when the iron-base sintered alloy material is used for a valve seat insert, wear-resistance can be improved, aggressiveness to mated material can be reduced, and mechanical strength can be improved, simultaneously.